The go-ahead has been given for the first trials of an HIV vaccine developed by scientists studying immunity in Kenyan prostitutes.

However, even if these early studies go well, it could still be a decade before a mass-produced vaccine could be produced.

Any delay would be unconscionable

Dr Seth Berkley, International Aids Vaccination Initiative

The joint project in Oxford and Nairobi observed that some prostitutes in Kenya, despite frequent unprotected sex with HIV-positive men, never seemed to pick up the virus themselves.

Their vaccine is based on the qualities which gave the women apparent resistance.

The trials, announced on Tuesday at the 13th International Aids Conference in Durban, are expected to begin in the UK later this summer. At this stage only the safety of the vaccine is under examination, not its effectiveness.

Scientists will be evaluating whether it has any adverse effects on the body.

Hundreds of millions of lives

Dr Seth Berkley, President of the International Aids Vaccine Initiative, said that time was now of the essence.

Professor Andrew McMichael is developing the vaccine

He said: "Given the fact that there is no treatment readily available and that this disease is 100% fatal, we are talking about hundreds of millions of lives if we don't get a vaccine as soon as possible.

"That is why any delay would be unconscionable."

The Oxford University team was reportedly "dismayed" earlier this year when some of the former prostitutes appeared to lose their immunity and contracted HIV.

Some believe that it was the constant exposure to the virus which allowed them to develop the immunity, and on stopping work, they became vulnerable.

The vaccine would only target one strain of the HIV virus.

However, the Oxford team is hopeful if the vaccine is a success, the technology can be modified to tackle all the different strains of HIV.

Lead researcher Professor Andrew McMichael said: "It would be very straightforward to make a similar vaccine based on the other strains, or even start mixing these different vaccines together to make a universal vaccine."

Liberal Democrat MP Dr Evan Harris has volunteered as one of the first guinea pigs given the vaccine.

Scientists aiming to produce Aids vaccines face a variety of problems, not least the mutating nature of the virus.

Different areas of the globe have different types of HIV, meaning that differently formulated vaccines would need to be produced for Africa.

As any vaccine will take years to develop, doctors are urging governments to do all they can to encourage safer sex , as well as give anti-retroviral therapies which prevent mother to child transmission, and may reduce the chance of adult to adult transmission.

The US government may be about to increase its budget aimed at stopping the spread of HIV in the developing world.

On Wednesday, Congress is due to debate plans to add $100m to a $200m annual budget .

'Beginning of epidemic'

Dr Evan Harris has volunteered to test the vaccine

But Sandra Thurman, head of the White House Aids Office said: "The US cannot do it alone. With no vaccine or cure in sight, we are at the beginning of an epidemic, not the end of an epidemic."

In the UK, Overseas Development Minister Clare Short criticised the attention paid in South Africa to prevention programmes.

She told BBC Radio 4's Today programme: "The South African government in general has been slow to have a real public education programme, prevention, availability of condoms and better care for people who are infected.

"They are starting to move now, and that is good."

She said that while the overall UK government spend on preventing the spread of Aids had increased, it could not afford simply to "sprinkle money around".